AB1394 INTRADISCAL CUTIBACTERIUM ACNES DECIDE ON INNATE AND ADAPTIVE IMMUNE PATHWAYS IN MODIC TYPE 1 CHANGES
Authors: I. Heggli, T. Mengis, L. Opitz, N. Herger, C. Laux, F. Wanivenhaus, J. M. Spirig, M. Betz, B. Aradi-Vegh, M. Farshad, O. Distler, S. Dudli
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Modic type 1 changes (MC1) are painful vertebral bone marrow (BM) edema of unclear etiology. Besides mechanical aspects, animal studies show the plausibility for two biological etiologies. In the bacterial etiology, <i>Cutibacterium acnes</i> (<i>C. acnes</i>) invades damaged intervertebral discs (IVDs) resulting in IVD infection and endplate damage. IVD-derived pro-inflammatory cytokines and virulence factors can consequently drain into the adjacent BM and induce an inflammatory response. In the autoimmune etiology, IVD and endplate damage expose immune privileged IVD cells and matrix to BM leukocytes, which react with an autoimmune response. <h3>Objectives</h3> To show that intradiscal <i>C. acnes</i> load is decisive for the pathomechnisms in MC1 bone marrow. <h3>Methods</h3> In a first study population, degenerated IVDs adjacent to a MC1 and not adjacent to a MC1 lesion were collected and <i>C. acnes</i> copy numbers/gram tissue (CCN) were quantified. The upper 99 % confidence interval (CI) limit in the control group was defined as threshold that distinguishes the two etiologies. From a second study population of MC1 patients, a MC1 and an intra-patient control BM aspirate, and the MC1 adjacent IVD was obtained from each patient. IVD CCN were determined, the etiology was assigned, and bulk RNA sequencing from total BM cells was performed. MC1 gene expression was normalized to intra-patient control and then compared between etiologies. Differentially expressed genes (DEGs) (p &lt; 0.01, log2 fold-change &gt; |0.5|) were identified and gene set enrichment analysis (GSEA) was performed. From a third study population, BM aspirates and IVDs were obtained. IVD CCN were quantified, ten pro- and anti-inflammatory and pro-fibrotic BM plasma proteins were quantified with ELISA, and RNA sequencing of CD45<sup>+</sup>CD66b<sup>+</sup> sorted BM neutrophils was performed. BM plasma protein concentrations were clustered and compared between cluster with Mann-Whitney test, and overrepresentation analysis (ORA) of DEGs between MC1 and intra-patient control BM neutrophils was determined. <h3>Results</h3> Of the first study population, the median CCN of control IVDs (n = 10) was 388 (interquartile range (IQR): 118-685)) and the upper 99 % CI limit was 870. MC1 IVDs (n = 30) had similar median CCN overall (Mann-Whitney: p = 0.29, 464 (229-1614)), but eleven samples (36 %) had &gt; 870 CCN (2659, (899-12900)), which was unique to MC1 IVDs and indicated a bacterial etiology (<b>Fig. 1a</b>). From a second study population, three MC1 patients from the bacterial (the three with the lowest CCN) and three from the autoimmune (the three with highest CCN) etiology were selected. Bulk RNA sequencing revealed 222 DEGs between the bacterial and the autoimmune etiology. GSEA showed enriched "neutrophil mediated immunity" and "granulocyte activation" in the bacterial and "adaptive immune response", "B- and T-cell activation" in the autoinflammatory etiology, pointing towards innate immune system contribution in the bacterial, and adaptive immunity in the autoimmune MC1 etiology (<b>Fig. 1b</b>). In the third population, MC1 to intra-patient control normalized BM plasma protein concentrations of the ten measured proteins were visualized using UMAP dimensionality reduction technique. Thereby, two patient clusters could clearly be distinguished (<b>Fig. 1c</b>). To identify whether clusters represented patients of different etiologies, CCN were compared between clusters and found to differ strongly (cluster 1: 351, (325, 387) vs. cluster 2: 2848, (1355, 3339)). Cytokine analysis between clusters showed upregulated neutrophil associated cytokines in cluster 1 vs. cluster 2 (IL-8: 16 pg/ml, (1, 54) vs. -15 pg/ml, (-21, -11), p = 0.004; ENA-78: 91 pg/ml (-5, 456) vs. -25 pg/ml, (-137, -21), p = 0.048), and a BM neutrophil "defense response to bacterium" in cluster 1, but not in cluster 2, further supporting that clusters represent different etiologies. <h3>Conclusion</h3> We show that IVD <i>C. acnes</i> load is decisive for the etiology-specific MC1 pathomechanisms. This has important clinical implications, as different MC1 etiologies might require different treatment strategies. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Irina Heggli: None declared, Tamara Mengis: None declared, Lennart Opitz: None declared, Nick Herger: None declared, Christoph Laux: None declared, Florian Wanivenhaus: None declared, Jose Miguel Spirig: None declared, Michael Betz: None declared, Borbala Aradi-Vegh: None declared, Mazda Farshad: None declared, Oliver Distler Speakers bureau: Bayer, Boehringer Ingelheim, Janssen, Medscape, Consultant of: 4P-Pharma, Abbvie, Acceleron, Alcimed, Altavant Siences, Amgen, AnaMar, Arxx, AstraZeneca, Baecon, Blade, Bayer, Boehringer Ingelheim, Corbus, CSL Behring, Galapagos, Glenmark, Horizon, Inventiva, Kymera, Lupin, Miltenyi Biotec, Mitsubishi Tanabe, MSD, Novartis, Pfizer, Prometheus, Redxpharna, Roivant, Sanofi and Topadur, Grant/research support from: Kymera, Mitsubishi Tanabe, Boehringer Ingelheim, Stefan Dudli: None declared.